Patent ductus arteriosus is a condition resulting from the partial continuation of fetal circulation. A fetus does not use its own lungs to oxygenate its blood, rather the fetus' blood bypasses the lungs and is oxygenated by the placenta. The ductus arteriosus allows blood to flow between the pulmonary artery and aorta in utero bypassing the non-functioning lungs during fetal development. Normally, the ductus arteriosus conduit closes naturally. This is prostaglandin dependent. If the ductus remains open, the infant has pathological shunting of blood from the systemic to the pulmonary system. This results in pulmonary hypertension which if uncorrected can result in the infant's disability and death.
Surgical procedures have been developed for closing the ductus which involve open heart surgery. The chest of the infant is opened to expose the ductus. A suture is tied around the ductus to seal it closed. For obvious reasons, open heart surgery is not desirable if alternatives exist.
Although other methods of occluding defects, most notably the use of a plastic plug to occlude the defect, were suggested as early as the 1950's, such methods similarly require the use of open heart surgery to access the defect and place the prosthetic implant.
Beginning in the early 1970's, a number of devices and methods were proposed for the percutaneous transluminal catheterization procedure for the repair of intracardiac defects. For example, U.S. Pat. No. 3,874,388 to King, et al., describes a device in which a pair of umbrella-like occluders are positioned on opposite sides of a defect and drawn and locked together at a central hub which crosses the defect. Although the King device and method proposed to eliminate the need to perform open heart surgery, use of the device was complicated in that generally the device required the umbrella-like occluders to be opened manually once positioned at the defect.
Collagen-containing connective tissue is ubiquitous in the human body and demonstrates several unique characteristics not found in other tissues. It provides the cohesiveness of the musculoskeletal system, the structural integrity of the viscera as well as the elasticity of integument. Intermolecular cross links provide collagen connective tissue with unique physical properties of high tensile strength and substantial elasticity. A previously recognized property of collagen is shrinkage of collagen fibers when elevated in temperature. This unique molecular response to temperature elevation is the result of rupture of the collagen stabilizing cross links and immediate contraction of the collagen fibers to about one-third of their original linear dimension. Additionally, the caliber of the individual fibers increases greatly, over four fold, without changing the structural integrity of the connective tissue.
There has been discussion in the existing literature regarding alteration of collagen connective tissue in different parts of the body. One known technique for effective use of this knowledge of the properties of collagen is through the use of infrared laser energy to effect tissue heating. The use of infrared laser energy as a corneal collagen shrinking tool of the eye has been described and relates to laser keratoplasty, as set forth in U.S. Pat. No. 4,976,709. The importance of controlling the localization, timing and intensity of laser energy delivery is recognized as paramount in providing the desired soft tissue shrinkage effects without creating excessive damage to the surrounding non-target tissues.
Another known technique of altering collagen is described in U.S. Pat. No. 5,458,596 to treat joints. U.S. Pat. No. 5,437,664 describes using a catheter for venous occlusion and coagulation of blood, but does not contemplate treating patent ductus arteriosus by shrinking the vessel to closure.